1. Field of the Invention
The present invention relates to an ink jet printer or recorder for forming an image by ejecting ink from its ink jet head. Specifically, the invention relates to an ink jet printer which makes it possible to suck and remove bad or defective ink, foreign substances, air bubbles, and/or the like from the ink jet head with the head nozzle capped.
2. Description of Related Art
A conventional ink jet printer of this type includes an ink jet head, which has a nozzle for ejecting ink and ink chambers storing ink behind the nozzle. By generating pressure vibration in one or more the ink chambers, it is possible to eject ink from the nozzle to form an image on a recording medium.
The printer also includes a cap for covering the outer side of the nozzle airtightly. The printer further includes a suction device, which may be a suction pump, for developing negative pressure in the cap in airtight contact with the nozzle to suck ink from the nozzle. The negative pressure developed in the cap covering the nozzle can suck and remove bad ink, foreign substances, air bubbles and/or the like from the nozzle. It is therefore possible to prevent defective ejection of ink from the nozzle so that a clear image can be formed.
On the other hand, negative pressure is applied always to the ink chambers and the nozzle. This negative pressure prevents ink from leaking from the nozzle, and allows ink to be ejected only when pressure vibration develops in one or more of the chambers. This prevents recording media from staining or spotting. The negative pressure may, however, worsen the suction and removal with the pump for the reason stated below.
FIGS. 5A-5D of the accompanying drawings show the suction and removal process as part of the maintenance of a conventional ink jet printer. The printer includes an ink jet head 73, which includes a nozzle plate 75 having a nozzle 75a for ejecting ink. The head 73 has ink chambers 77a storing ink behind the nozzle plate 75. The chambers 77a are connected to the nozzle 75a. The head 73 also includes actuators 77 including piezoelectric elements. Each of the actuators 77 is associated with one of the chambers 77a. The head 73 further includes a manifold 79 connected to the chambers 77a. The manifold 79 is also connected through a tube (not shown) or the like to an ink tank (not shown) for supplying the chambers 77a with ink. When one or more of the actuators 77 are energized to generate pressure vibrations in the associated chambers 77a, ink is ejected from the nozzle 75a.
This printer also includes a cap 83 for compressively contacting the nozzle surface 75b of the nozzle plate 75 to airtightly cover the outer side of the nozzle 75a. The cap 83 has a suction port 83a connected to a suction pump (not shown). When the pump is driven, negative pressure develops in the cap 83.
As shown in FIG. 5A, air bubbles 99 may be produced in the ink chambers 77a. As shown in FIG. 5B, it is possible to suck and remove the bubbles 99 together with ink by capping the nozzle 75a with the cap 83 and driving the pump.
On the other hand, negative pressure is applied always to the ink chambers 77a and nozzle 75a. Immediately after the pump stops, as shown in FIG. 5C, this negative pressure may draw back into the ink jet head 73 some of the bubbles 99 sucked already into the cap 83. Even after the suction ends and the cap 83 separates from the head 73, as shown in FIG. 5D, air bubbles 99 remain in the head, and may cause defective ejection of ink from the nozzle 75a. Not only the bubbles 99 but also foreign substances and/or solidified ink may be drawn back into the head 73, and cause defective ejection of ink.